This invention relates to an improvement of a bar code recognition apparatus.
Bar codes in common use nowadays are based on the JAN (Japan Article Number) as depicted in FIG. 1. Each of these bar codes consists of a first group 1 of characters, a second group 2 of characters, center bars 3, left bars 4, and right bars 6. The first group 1 consists of six characters, and the seccnd group 2 consists of five characters and one digit modulus check character 8. The center bars 3 are positioned between the first group 1 and second group 2. The left bars 4 are on the left side of the first group 1, and the right bars 6 are on the right side of the second group 2. Each bar code is separated from the preceding bar code by a left margin 5 and from the following bar code by a right margin 7.
The six characters of the first group 1 represent numerals 0 to 5, respectively. The five characters of the second group 2 represent numerals 6, 7, 8, 9 and 0, respectively. Each of these eleven characters is comprised of two white bars and two black bars, which are alternately arranged.
FIG. 2 shows a concordance between numerals 0 to 9 and the eleven characters of the bar code shown in FIG. 1. Each character is expressed by seven bits. Any bit "0" corresponds to a white bar, and any bit "1" corresponds to a black bar. Any consecutive bits "0" are represented by a thicker white bar, and any consecutive bits "1" are represented by a thicker black bar. In other words, the wider each bar, the more bits. Each character of the first group 1 is represented by two kinds of data, using both odd and even parities, whereas each character of the second group 2 is expressed only by data of even parity. Since data of odd and even parities are used to express the six characters of the first group 1, the number of possible decimal modes of expression is increased and the applicable fields for the characters is broadened.
The bar codes as explained above have been widely used in POS (Point of Sales) systems. Once prices of commodities expressed in bar codes are read, the totals of prices of commodities sold can be calculated rapidly and efficiently. To read such bar codes, a fixed scanner 10 shown in FIG. 3 and disclosed in U.S. Pat. No. 3,988,573, or a manual scanner such as a light pen has been used. The manual scanner is subject to variations related to the speed of scanning a bar code so that a pattern electrically formed as the result of reading a bar code may often change the width of the bars, which causes misrecognition of the bar code. Particularly, if bar codes such as JAN, which have four kinds of bar widths (or control width, double, triple and guadruple width), are to be recognized, it is not possible to determine whether a width value which is generated in a reader is correct or is a changed value. Thus, a correct recognition of bar codes cannot be achieved.